The art of metrology includes various methods and apparatus for examining sample characteristics. Some of these apparatus and methods are destructive, such as scanning electron microscopy (SEM) and some are non-destructive, such as scatterometry (e.g., ellipsometry and reflectometry). There are also some apparatus that can be employed in non-destructive mode and destructive mode, such as scanning probe microscopy (SPM) (for example, atom force microscopy (AFM) and magnetic force microscopy (MFM)).
There are numerous suggestions in the prior art to employ any of the above apparatus and methods to sample metrology. For example, in U.S. Pat. No. 6,489,611 to B. D. Aumond and K. Youcef-Toumi the inventors teach AFM for profiling high aspect ratio samples. They also describe a deconvolution technique for deconvolving the sample image and a technique for measuring the tip radius of curvature. U.S. Pat. No. 6,650,423 to R. J. Markle et al. teaches application of scatterometry techniques, such as reflectometry or ellipsometry, to a method for determining dimensions in a test structure that has a number of trenches and columns defined in the trenches. U.S. Pat. No. 6,602,723 to R. J. Markle presents a method of incorporating metrology grating into die design. J. H. Hussey et al. explain a method and apparatus for run-to-run control of trench profiles in U.S. Pat. No. 6,728,591. According to their teaching, a trench metrology data from the processed wafer is acquired. Then a chamber characteristic adjustment process is performed in response to the trench metrology data and the data relating to the processing chamber characteristic. A feedback adjustment of the processing chamber is performed in response to the chamber characteristic adjustment process. Furthermore, P. A. Burke in U.S. Pat. No. 6,000,281 discloses an integrated stylus with AFM to carry out quick, non-destructive, inexpensive measurements of critical dimensions (CDs).
Although the above references teach many useful approaches to metrology, they cannot be used to construct an efficient, low-cost and fast metrology tool that is primarily non-destructive. To provide a more rapid and versatile metrology system, S. G. Muckenhirm suggests in his U.S. Pat. No. 6,986,280 that AFM/SEM be integrated with a scatterometer. The scatterometer can rapidly measure to indicate whether a problem exists, and the AFM can perform detailed measurements on wafers flagged by the scatterometer. Furthermore, in U.S. published applications 2005/0128489 and 2006/0064280 Bao et al. and Vuong et al. teach an optical metrology model that optimizes the method based on the goals. Additional references include U.S. published application 2004/0080757 to Stanke et al. and U.S. Pat. No. 6,658,922 to Leigh et al.
Of the various AFM/SEM and related measurements employing a scanning probe many are described in the prior art. For further references specific to various techniques related to AFM in particular the reader is referred to the following U.S. Pat. Nos.: 5,017,007; 5,994,691; 6,052,238; 6,194,711; 6,441,359; 6,621,079; 6,643,012; 6,668,628; 6,850,323 and 7,032,427.
Many of the more recent teachings listed above and referenced therein suggest that a combination of techniques would be beneficial for rapid and efficient sample metrology. Unfortunately, none of the teachings solve the problem of an effective and fast combination of optical and scanning probe measurements to yield an efficient, low-cost and fast metrology system.